One conventional method of forming a refrigeration apparatus cabinet is to provide an inner liner wall and an outwardly spaced outer cabinet wall. Insulation is provided in the space between the two walls by foaming in place a foam insulation material, such as polyurethane. A problem arises in conventional such cabinet constructions in that the foam-in-place insulation tends to adhere to the liner wall. The liner wall is conventionally formed of a synthetic resin, such as high impact polystyrene (HIPS) or acrylonitrile-butadiene-styrene (ABS), etc. resins. The adhesion of the foam-in-place insulation to the synthetic liner wall can cause stress cracking thereof as a result of the differential thermal expansion of the insulation and liner wall plastic material.
Weiss et al. U.S. Pat. No. 3,960,631, assigned to the assignee hereof, disclose an improved liner construction wherein a foam release agent is provided on the plastic liner sheet prior to the forming thereof against the liner configuration to solve the above problem. Benford U.S. Pat. No. 4,707,401 addressed the problem by using a bilayer film having a controlled limited bond with a synthetic resin liner so as to effectively prevent stress cracking thereof. The film, however, further had a strong, absolute bonding to the foam-in-place insulation so that a desirable double-stress skin laminate is effectively provided.
The polyurethane foam insulation used in the above-described cabinets used a chloroflorocarbon (CFC) blowing agent. In fabricating the cabinets, CFCs are released to the atmosphere. Further, even after the cabinet is complete, CFCs can diffuse from the cabinet to the atmosphere. Recently, concern has arisen that CFCs deplete the ozone layer from the atmosphere. This damages the atmosphere since the ozone layer filters harmful ultraviolet radiation from sunlight. As a result, a strong demand has arisen to restrict the use of CFCs in refrigeration apparatus.
As a result of the above problems with CFCs, some manufacturers of refrigeration apparatus cabinets are switching to the use of polyurethane foam including hydrochloroflorocarbon (HCFC) blowing agents. However, a further problem is evident resulting from switching from use of CFC to HCFC. This problem relates to the detrimental effect to the plastic liner caused by the HCFC. Particularly, with an ABS plastic liner, the HCFC can cause brittling and cracking of the liner; while with HIPS liners, the HCFC can cause blistering. Either of these results is undesirable.
The present invention is directed to solving one or more of the problems discussed above, in a novel and simple manner.